This application relates to a method for imparting fire-retardant properties to glass-filled polycarbonate resins, to compositions useful in the method, and to fire-retarded polycarbonate resins of the type produced by the method.
Because of their strength, glass-filled polycarbonate resins have a great many significant commercial applications. They are especially useful for injection molding of thin walled parts. Unfortunately, glass-filled polycarbonate resins are inherently flammable and can drip hot molten material causing nearby materials to catch fire as well. Thus, in order to safely utilize glass-filled polycarbonates in many applications it is necessary to include additives which retard the flammability of the material and/or which reduce dripping. The challenge is to identify additives which accomplish this purpose without compromising the desirable strength properties, without introducing new problems (such as the potential environmental problems associated with some halogenated additives) and without prohibitively increasing the price.
A variety of different materials have been described for use in producing fire-retarded and/or drip-resistant polycarbonate compositions. Exemplary of these are the materials described in U.S. Pat. Nos. 3,971,756, 4,028,297, 4,110,299, 4,130,530 4,303,575, 4,335,038, 4,552,911, 4,916,194, 5,218,027 and 5,508,323. Notwithstanding these varied disclosures, however, there remains room for improvement in the formulation of fire-retrarded glass-filled polycarbonate resin compositions.
Among the additives which are widely used commercially in fire-retarded polycarbonate resin compositions are organic salts, particularly sulfonic acid salts. Particular examples of these salts are perfluoroalkane sulfonates, such as potassium perfluorobutane sulfonate (“KPFBS”, also known as “Rimar salt”) and potassium diphenylsulfone sulfonate (“KSS”). The use of perfluoroalkane sulfonates in polycarbonate resins is described in U.S. Pat. No. 3,775,367. However, the benefits which can be obtained using these materials alone with glass-filled polycarbonate resins are limited and indeed additional additives are generally included. The conventional means for enhancing the fire-retardant properties of these types of compositions has been the addition of soluble organic halogen additives. However, the halogenated additives are unsuitable for compositions that are required to meet certain newer “ECO-friendly” standards.